Samsung's documentation leaves a bit to be desired, though it's hard to explain the option without getting too technical.
Summary: if it's grayed out, it doesn't apply to that device. Most people will only see it enabled for game consoles like the 360 or PS3, or if using a computer over HDMI.
Long explanation:
Briefly, there's two different ways of encoding colors in video signals -- YCrCb and RGB. YCrCb is what has been used for video forever, and there is no ambiguity in the range it uses. Most devices use this (including cable boxes, DVD players, and blu-ray).
Computers use a different encoding scheme called RGB. To complicate matters, some video devices use RGB as well. But video devices that use RGB use a different level than most computers. Since there's same ambiguity in the levels the device might be using, Samsung gives you the HDMI black level option which tells the TV which set of levels a device is using.
TV = Samsung FPT 5084 Plasma
I have 2 DVD's linked with HDMI cables yet the below menu item is always 'greyed' out and I am unable to adjust. Anyone know why???
Setting the HDMI Black Level
Use this function to adjust the Black Level of the picture while in HDMI mode.
➢ This function is active only when an external device is connected to a TV via HDMI.

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